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Income Taxes - Components of Income Tax Expense (Details) - CAD ($) $ in Millions |  |  |  |  |  | 12 Months Ended
--- | --- | --- | --- | --- | --- | ---
Jan. 01, 2022 | Jan. 01, 2021 | Dec. 09, 2020 | Jan. 01, 2020 | Jul. 01, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |
Current income tax expense |  |  |  |  |  | $ 35 | $ 35 | $ 28
Deferred income tax expense (recovery) related to the origination and reversal of temporary differences |  |  |  |  |  | (95) | 22 | (61)
Deferred income tax expense related to temporary difference on investment in subsidiary |  |  |  |  |  | 9 | 0 | 0
Deferred income tax expense resulting from changes in tax rates or laws expense (recovery) |  |  |  |  |  | (7) | (31) | 0
Writedown (reversal of writedown) of deferred income tax assets |  |  |  |  |  | 8 | (9) | 27
Current income tax expense |  |  |  |  |  | 35 | 35 | 28
Deferred income tax recovery |  |  |  |  |  | (85) | (18) | (34)
Income tax expense (recovery) |  |  |  |  |  | $ (50) | $ 17 | $ (6)
Corporate tax rate |  |  |  |  |  | 24.50% | 26.50% | 26.80%
ALBERTA |  |  |  |  |  |  |  |
Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |
Corporate tax rate |  | 9.00% | 8.00% | 10.00% | 11.00% | 8.00% | 11.00% |
ALBERTA | Forecast |  |  |  |  |  |  |  |
Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |
Corporate tax rate | 8.00% |  |  |  |  |  |  |

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- Definition The applicable income tax rate. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2019-01-01 -Paragraph 81 -Subparagraph c -Clause ii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_c_ii&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of income taxes payable (recoverable) in respect of the taxable profit (tax loss) for a period. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 12 -IssueDate 2019-01-01 -Paragraph 80 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_80_a&doctype=Standard -URIDate 2019-03-27 + Details
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